As people age, their eyes are less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Contact lenses can be worn to address presbyopia. In one type of such lenses, distance and near vision regions are concentrically arranged around the geometric center of the lens. Light passing through the optic zone of the lens is concentrated and focused at more than one point in the eye.
In another type of lens, a segmented lens, near and distance vision regions are not concentric about the geometric center of the lens. The wearer of the segmented lenses is able to access the near vision region of the lens because the lens is constructed to allow it to translate, or move vertically relative to the pupil of the wearer's eye. The lens moves vertically when the person wearing the lens shifts their gaze downwardly to read. This upwardly positions the near vision portion in the center of the wearer's gaze. Essentially all of the light passing through the optic zone can be focused at a single point in the eye based on gaze.
A common type of translating lens has a truncated shape. That is, unlike most lenses that are completely circular or oval, the lower portion of the truncated contact lens is flattened as by cutting off or shortening that part of the lens. Exemplary references to such lenses include U.S. Pat. No. 7,543,935, incorporated herein by reference. Other designs may be circular or elliptical but, in such cases, have other design features to enable them to move on the eye with gaze change. Improving the translational properties of translating contact lenses is desirable.
Another type of translating lens has an outer shape which is continuously circular or oval, but contain a substantially thickened portion peripheral to the central optical zone. This thickened portion is intended to contact the lower lid and translate with blink. Exemplary references to such a lens are described in U.S. Pat. No. 7,040,757 and U.S. 20100171924, incorporated herein by reference. In these examples, the thickness in the peripheral portions of the lens outside the optical zone is substantially uniform for meridians parallel to the vertical meridian of the lens, and a lens according to this invention exhibits mirror symmetry with respect to a plane cutting through the vertical meridian. Unfortunately, this will not lead to the intended translation when worn on an eye.
In another type of contact lens, a silicone hydrogel material is employed. These materials may be used in single vision lenses or translating designs, and they have the advantage of providing increased transmission of oxygen to the ocular tissues, but they may not move with blink on the eye as readily as other contact lenses. Exemplary references to such a material are described in U.S. Pat. No. 6,099,852, incorporated herein by reference. Improving the movement of silicone hydrogel contact lenses is desirable.